Method and apparatus for breaking up and separating waste glass to obtain cullet

ABSTRACT

An apparatus for breaking up and separating waste glass to obtain cullet comprising a grizzly made up of parallel bars arranged at a spacing smaller than the minimum width of projection of three-dimensional extraneous matter and auxiliary parallel bars disposed over one surface of the grizzly and arranged at right angles to the bars to form a lattice, the diagonal dimension of the openings of the lattice being smaller than the maximum width of projection of planar extraneous matter. The lattice is in the form of a rotatable drum with the grizzly positioned on the inner side of the its peripheral portion. The drum-shaped lattice has scraper plates attached to its inner periphery and an inlet for the waste glass and an outlet for the extraneous matter at its opposite ends respectively. The parallel bars can be arranged either annularly or axially with the auxiliary parallel bars being arranged oppositely.

This is a divisional of application Ser. No. 741,490, filed Nov. 12,1976, which has issued on Jan. 24, 1978 as U.S. Pat. No. 4,069,979.

BACKGROUND OF THE INVENTION

The present invention relates to a method and an apparatus for breakingup and separating waste glass to obtain cullet.

Recycled waste glass contains caps and the like of glass bottles and mayfurther contain empty bottles for beverages. In recent years, many ofcaps are made of aluminum, while some are made of iron, synthetic resin,cork, etc. Empty cans are generally aluminum and iron cans. When wasteglass containing such extraneous matter is used as cullet, the glassproduct obtained contains bubbles and unmelted substances, i.e.so-called "stones," and involves changes in color or transparency due tothe presence of the extraneous matter. These objections reduce thestrength and appearance of the product, seriously impairing commercialvalue of the product.

Accordingly the extraneous matter must be removed to the greatestpossible extent. However, the extraneous matter varies greatly in shapeand properties. Moreover, regardless of whether the waste glass has beenfractured or not, some kinds of extraneous matter may not differ fromthe waste glass in shape, size or specific gravity. Thus the undesirablematter is not readily separable by the conventional methods such asscreening, washing with water, sink and float separation, etc., with theexception of magnetic materials which are magnetically separable. Infact, the conventional methods give very low yields. For this reason,for the preparation of cullet, extraneous matter is usually removed fromthe waste glass by manually roughly breaking waste glass, separating offsoil, sand, mud and like fine particles by screening, washing theoversize pieces with water to remove paper, cork and synthetic resinextraneous materials, and further manually removing caps, empty cans andother extraneous pieces while magnetically separating off magneticmaterial. However, the usual method involves the cumbersome andinefficient manual separation step and still permits a large amount ofextraneous matter to remain in the waste glass.

On the other hand, because finely divided glass produces bubbles whenmelted in the furnace and because of the necessity of assuring effectiveand efficient operation of the optical color separator (such as SOTEX31) used to obtain good cullet, glass pieces must have sizes within aspecified range (e.g. -20 to +5 mm). For this purpose, waste glass inconventionally broken up with use of jaw crushers and impeller breakersfor ore and stone, instead of resorting to an inefficient manualbreaking procedure. However the operation with use of such crusherstends to cause abrasion and compression, consequently impairing thequality of cullet or reducing the yield.

SUMMARY OF THE INVENTION

An object of this invention is to provide a method and an apparatus forbreaking up and separating waste glass by which various kinds ofextraneous matter can be removed from the waste glass efficiently by asimple procedure to obtain a high yield of cullet in broken pieceshaving sizes within the desired range.

Another object of this invention is to provide a simple, compact andautomatic apparatus by which a large amount of waste glass can be brokenup and separated repeatedly, continuously and efficiently with use of alattice having two different surface levels so as to remove extraneousmatter from the waste glass with improved efficiency and to break up thewaste glass to pieces of cullet with improved effectiveness.

This invention has been accomplished based on our findings describedbelow.

First, the extraneous matter contained in waste glass is not brittle, islightweight and involves small energy of impact when falling, so thatthe extraneous matter remains unbroken in shape when dropped undergravity. Grizzlies comprising parallel bars arranged at a specifiedspacing are of such nature that they permit passage of planar piecessuch as glass pieces (including extraneous pieces of planar shape suchas pull-top pieces) but retain thereon three-dimensional extraneousmatter. Further when brittle glass is dropped onto a grizzly, the barsproduce concentrated stress in the glass, allowing greater pieces ofglass to break up under gravity, whereas smaller glass pieces whichinvolve small energy of impact remain unbroken. When dropped onto thegrizzly and thereby broken, waste glass can be separated into glasspieces as an undersize material and extraneous matter as an oversizeportion. Thus cullet is obtainable by a simplified procedure free ofexcessive breaking, while permitting extraneous matter to remainseparate and loose without engaging glass pieces. Consequently, the useof the grizzly achieves improved yields and facilitates after treatment(such as sink and float separtion for the removal of the remainingextraneous matter and color separation) required for the preparation ofgood cullet.

Second although extraneous matter which is three-dimensional relative tothe glass pieces to be recovered as cullet is removable by suitablydetermining the spacing between the bars of the grizzly, it is difficultto remove aluminum pull-top pieces (removed from containers to openthem) which are nearly as planar as glass pieces, flat covers ofcup-shaped glass containers, synthetic resin caps, aluminum ringsremaining on the mouth of glass bottles for alcoholic drinks, etc.Accordingly, these extraneous matter must be removed usually by aftertreatment. However, when waste glass is dropped onto a latticecomprising the grizzly and auxiliary parallel bars disposed over thenon-breaking surface thereof and arranged at right angles to theparallel bars of the grizzly, extraneous matter of planar shape is alsoremovable without impairing the breaking an separating ability of thegrizzly.

This invention provides a method of breaking up and separating wasteglass with use of a lattice comprising a grizzly made up of parallelbars arranged at a spacing smaller than the minimum width of projectionof three-dimensional extraneous matter and auxiliary parallel barsdisposed over one surface of the grizzly and arranged at right angles tothe bars, the diagonal dimension of the openings of the lattice beingsmaller than the maximum width of projection of planar extraneousmatter, the method being characterized by dropping the waste glass ontothe grizzly surface of the lattice to breakup the waste glass on thegrizzly under gravity an to separate the waste glass into an undersizeportion of the waste glass passing through the lattice and an oversizeportion containing large pieces of waste glass and various kinds ofunbroken extraneous matter, and repeatedly subjecting the oversizeportion to the aforesaid operation to obtain cullet as an undersizematerial and to remove the extraneous matter from the waste glass as anoversize material.

According to the method of this invention the surface of the grizzly ispositioned above the auxiliary parallel bars, serving as a first surfacefor breaking up the waste glass under gravity. Large pieces of wasteglass involving great energy of falling impact are efficiently broken bythe grizzly surface, whereas the smaller the pieces, the smaller is theenergy of falling impact and therefore the less likely it is for them tobe broken. The surface of the auxiliary parallel bars below the grizzlysurface provides a second surface for breaking up the waste glass undergravity. Many pieces of waste glass first fall onto the grizzly surfaceand then onto the auxiliary parallel bars. At this time, since theenergy of falling impact involved has already been almost nullified whenthe glass pieces strike the grizzly surface, relatively large pieces ofglass alone are broken on the auxiliary parallel bars. On the otherhand, the glass pieces falling directly onto the auxiliary bars arebroken to the same extent as on the grizzly surface. Thus the latticeassures a higher breaking efficiency than when the grizzly alone isused. Moreover, the provision of the breaking surfaces at two differentlevels prevents excessive breaking of small glass pieces.

The openings of lattice defined by the grizzly bars and auxiliaryparallel bars regulate the passage of waste glass and extraneous matter,such that planar glass pieces and extraneous matter which are passablethrough the grizzly but larger than the diagonal dimension of theopenings are retained as an oversize portion. Consequently, such glasspieces are subjected to the breaking action again, while the extraneousmatter still remains as an oversize portion. Thus the planar extraneousmatter is removable as an oversize portion and the maximum size of theglass pieces obtainable as an undersize portion is controllable bysuitably determining the size of the lattice openings. The extraneousmatter which is not brittle remains unbroken and is protected from thefalling glass pieces by the parallel bars of the grizzly because theyare retained on the auxiliary bars as positioned between the grizzlybars. Accordingly rings and pull-top pieces are retained on the latticein shape without being collapsed.

The method carried out with use of the lattice gives cullet pieceswithin the desired size range with high efficiency in high yields,removes extraneous matter to a greatly increased extent, and facilitatesafter treatment such as separation of the remaining extraneous matterand color separation to produce satisfactory cullet.

Basically, the apparatus of this invention comprises the above-mentionedlattic disposed in the passage for dropping the waste glass. The latticeis in the form of a rotatable drum, with the guzzly defining the innerperiphery of the drum, having scraper plates attached to the innerperiphery, a glass inlet at one end of the drum and an outlet forextraneous matter at the other end thereof.

With the present apparatus, waste glass is continuously charged from theinlet. The waste glass is progressively sent toward the outlet whilebeing repeatedly raised by the scraper plates and dropped on the grizzlysurface. During this operation, the waste glass is broken up, and theglass pieces having sizes within the desired range pass through thelattice and recovered as cullet. The remaining extraneous matter iscontinuously forced out from the outlet and thereby separated from thecullet.

Accordingly a large amount of waste glass can be repeatedly broken upand separated with use of a single lattice by a continuous, automaticand therefore efficient operation.

The drum-type lattice is installed in an inclined position or is made ina tapered form to facilitate the movement of the waste glass andextraneous matter toward the outlet, thereby ensuring a smoothoperation, while preventing extraneous matter from being collapsed andrendered passable through the lattice.

Other objects and features of this invention will become apparent fromthe following discription with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view showing a preferred embodiment of the apparatusof this invention, one half of the same being in vertical section;

FIG. 2 is a cross sectional view of the same;

FIG. 3 is a fragmentary perspective view showing the same on an enlargedscale;

FIG. 4 is a cross sectional view of a modified embodiment in which thebars of a grizzly extend in a different direction;

FIG. 5 is a fragmentary perspective view of the same on an enlargedscale;

FIG. 6 is a fragmentary perspective view on an enlarged scaleillustrating how planar pieces of extraneous matter are separated;

FIG. 7 is a front view showing an embodiment of the tapered drum type;and

FIG. 8 is a front view showing an embodiment of the inclined drum type.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The apparatus of this invention comprises a lattice including a grizzly2 made up of parallel bars 1 arranged at a spacing smaller than theminimum width of projection of three dimensional extraneous matter suchas empty cans, and auxiliary parallel bars 3 disposed over the grizzly 2and arranged at right angles to the bars 1. The diagonal dimension ofthe openings of the lattice is smaller than the maximum width ofprojection of planar extraneous matter such as pull-top pieces, rings,flat caps, covers, etc. As seen in FIGS. 1 to 5, the lattice is in theform of a rotatable drum with the grizzly 2 defining the inner peripheryof the drum. Scraper plates 4 are attached to the inner periphery of thedrum. The drum has an inlet 5 for waste glass and an outlet 6 forextraneous matter at the opposite ends respectively.

With the embodiment shown in FIGS. 1 to 3, the bars 1 of the grizzly 2extend in the direction of rotation of the drum, while with theembodiment shown in FIGS. 4 and 5, the bars 1 extend at right angles tothe direction of rotation of the drum. FIG. 1 shows guide rollers 7,guide rails 8, a drive gear 9 and a driven gear 10.

When the drum-shaped lattice is rotated with waste glass placed therein,the glass is repeatedly raised by the scraper plates 4 and then droppedonto the grizzly 2. The larger the falling glass piece, the greater isthe energy of impact involved and the more likely is the glass piece tobe subjected to concentrated stress striking the bar 1. Thus large glasspieces are readily breakable, whereas small glass pieces are lessbreakable. The planar glass pieces which have such shape originally orwhich have been so shaped by being broken tend to pass through thegrizzly 2 relatively rapidly and are therefore placed on the auxiliarybars 3 because of their characteristic shape, even if the maximum widthof projection thereof is larger than the spacing between the grizzlybars 1. Among these glass pieces, those having a maximum width ofprojection which is approximately smaller than the spacing between theauxiliary bars 3 rapidly pass between the bars 3, namely through theopenings of the lattice.

On the other hand, pieces of extraneous matter fall at a relativelysmall velocity and involve smaller energy of falling impact. Because oftheir elastic nature, lightweightness an characteristic shapes, theywill not be broken nor be collapsed upon striking the lattice, whilethree-dimensional articles such as empty cans will not pass through thegrizzly 2. Planar pieces such as rings, pull-top pieces, flat caps orcovers, etc. tend to readily pass through the grizzly 2 and arepositioned on the auxiliary bars 3. However, their posture is sogoverned by the parallel bars 1 of the grizzly 1 that the maximum widthof projection thereof is at right angles to the auxiliary bars 3 as seenin FIG. 6. Consequently they are retained on the bars 3 and unable topass through the openings of the lattice.

Thus extraneous pieces of three-dimensional shape as well as of planarshape remain within the lattice as an oversize portion and arerepeatedly raised and dropped by the scraper plates 4 along with coarsepieces of waste glass. During this process, brittle waste glass alone isbroken up to smaller pieces, which passes through the lattice openings.The waste glass therefore progressively reduces in amount. Finally theextraneous matter alone remains. As a result, the waste glass is madeinto pieces of cullet not larger than a specified size, with theextraneous matter removed therefrom.

Because the remaining extraneous matter involves small energy of impactwhen falling, has an elastic nature and is protected from the impactexerted by falling glass pieces by being positioned between the parallelbars 1 of the grizzly 2, it remains in the form of separate pieceswithout being collapsed. Thus a very high proportion of the extraneousmatter remains within the lattice. Moreover, extraneous pieces will notengage and retain glass pieces Since the waste glass generally fallsonto the auxiliary bars 3 after falling onto the bars 1 of the grizzlyinstead of falling directly onto the former, small pieces of glass willnot be further broken. Glass pieces which are of such sizes that theyneed not be further broken strike the auxiliary bars 3 with their planardirection positioned vertically be being guided by the grizzly bars 1and readily as through the bars 3, so that they are less likely to bebroken by the bars 3. Accordingly glass pieces are broken up to sizeswithin a narrow range without entailing noticeable formation of fines orvery small pieces as is the case with use of the grizzly alone.

The auxiliary parallel bars 3 will not break the glass pieces other thanthose of large sizes falling directly thereagainst. The combination ofthe bars 3 and the grizzly in the form of a lattice having two differentsurface levels achieves the synergic effect of removing the extraneousmatter with greatly improved efficiency, without impairing the functionof the grizzly which gives broken pieces in a narrow size range, whileprotecting the extraneous matter from falling glass pieces. The effectto remove the extraneous matter can be ensured to the greatest extent byminimizing the spacing between the bars 3 within the range allowable inview of the size of the pieces of cullet to be obtained.

With the embodiment shown in FIGS. 1 to 3, glass pieces tend to slip onthe grizzly 2 and are likely to be subjected to an abrasive breakingaction, whereas in the case of the embodiment shown in FIGS. 4 and 5,glass pieces are less likely to slip by being caught by the parallelbars 1 and will not be broken by abrasion.

FIG. 7 shows a lattice in the form of a tapered drum, while FIG. 8 showsa drum-shaped lattice as installed in an inclined position. Theinclination of the grizzly surface causes the extraneous matter toprogressively move toward the outlet 6, automatically running of theextraneous matter. With the lattice of the tapered drum type shown inFIG. 7, the bars 1 or 3 extending axially thereof have a widthprogressively increasing from one end to the other so as to maintain auniform spacing between the bars in the axial direction.

Although the auxiliary bars 3 will not positively exert a breakingaction, excessive breaking can be eliminated more effectively when theyare made of elastic material such as steel strips.

Given below are experiments conducted according to this invention.

EXPERIMENT 1

A rotatable drum-shaped lattice, 1.5 m in diameter and 1.5 m in length,was used, the lattice comprising a grizzly made up of 20-mm-squareparallel bars and 20-mm-wide steel strips serving as auxiliary bars anddisposed over the grizzly. The lattice had openings, 20 mm × 20 mm, andwas equipped with four scraper plates and driven at 14 r.p.m. Theeffective height of the apparatus the waste glass was dropped was about1.3 m.

Waste glass (97.34 kg) consisting of 99.38% by weight of glass bottlesand sheet glass pieces and 0.62% by weight of caps, pull-top pieces andlike extraneous matter was placed into the apparatus, and the apparatuswas driven for 1.5 minutes. Table 1 shows the size distribution of theundersize material obtained and the amount of the extraneous mattercontained therein, in comparison with those of the starting testmaterial. The extraneous matter in the undersize material was a planersmall pull-top piece.

                  Table 1                                                         ______________________________________                                               Size distribution (wt. %)                                                     Test          Undersize                                                       material      material                                                 Size               Extraneous        Extraneous                               (mm)     Whole     matter    Whole   matter                                   ______________________________________                                        +40      18.4      0.17      --      --                                       -40 to +20                                                                             50.7      0.45      --      --                                       -20 to +10                                                                             23.1       0.0008   72.5    0.0008                                   -10 to +5                                                                               4.9      --        19.4    --                                       -5        2.9      --         8.1    --                                       Total (%)                                                                              100.0     0.62      100.0   0.0008                                            (97.34 kg)                                                                              (602.7 g) (94.81 kg)                                                                            (0.8 g)                                  ______________________________________                                    

The amount of the undersize material is

    (94.81/97.34) × 100 = 97.4 wt.%.

The amount of the glass recovered when the -20 mm to +5 mm portion wascollected as the final product is

    {0.974 × (1 - 0.081 - 0.000008) × 100}/0.9938 = 90.1 wt. %.

The amount of the extraneous matter contained in the final product is

    {0.8/(94.810 × 0.919)} × 100 = 0.0009 wt. %.

The amount of the extraneous matter removed is

    {(602.7 - 0.8 )/602.7} × 100 = 99.87 wt. %.

EXPERIMENT 2.

The apparatus used had the same construction as the apparatus ofExperiment 1 except that the spacing between the auxiliary parallel barsof strip steel was reduced to form lattice openings, 20 mm × 15 mm.Waste glass (86.51 kg) consisting of 99.57% by weight of bottles andsheet glass pieces and 0.43% by weight of caps, pull-top pieces and likeextraneous matter was placed into the apparatus, which was then drivenfor 1.5 minutes as in Experiment 1. Table 2 shows the size distributionof the undersize material obtained and the amount of the extraneousmatter contained therein, in comparison with those of the starting testmaterial. The extraneous pieces in the undersize material were smallplanar pieces such as rings of pull-top pieces and cutout portionsthereof as separated therefrom.

                  Table 2                                                         ______________________________________                                               Size distribution (wt. %)                                                     Test          Undersize                                                       material      material                                                 Size               Extraneous        Extraneous                               (mm)     Whole     matter    Whole   matter                                   ______________________________________                                        +40      17.0      0.15      --      --                                       -40 to +20                                                                             49.4      0.28      --      --                                       -20 to +10                                                                             26.2       0.0043   68.6    0.0004                                   -10 to +5                                                                               4.8      --        22.9    --                                       -5        2.6      --         8.5    --                                       Total %  100.0     0.43      100.0   0.0004                                            (86.51 kg)                                                                              (372.9 g) (83.29 kg)                                                                            (0.3 g)                                  ______________________________________                                    

The amount of the undersize material is

    (83.29/86.51) × 100 =  96.3 wt. %.

When the -20 mm to +5 mm portion was collected as the final product, theamount of the glass recovered is

    {0.963 ×(1 - 0.085 - 0.000004) × 100}/0.9957 = 88.5 wt. %.

The amount of the extraneous matter contained therein is

    {0.3/83290 × 0.915)}× 100 = 0.0004wt. %.

The amount of the extraneous matter revoved is

    {(372.9 - 0.3)/372.9} × 100 = 99.91 wt. %.

Comparison between Experiment 1 and Experiment 2 shows that the latterconducted with a reduced spacing between the auxiliary parallel barsremoved the extraneous matter much more effectively, although thepercent glass recovery was slightly lower due to an increase in theamount of fine to small pieces.

In either case, the amount of the extraneous matter contained in thefinal product is extremely small. Moreover, since the extraneous piecesare singly separated from the glass pieces, they are readily completelyremovable by sink and float separation or by manual separation. What weclaim is:

1. An apparatus for breaking up and separating waste glass to obtaincullet comprising a grizzly made up of parallel bars arranged at aspacing smaller than the minimum width of projection ofthree-dimensional extraneous matter and auxiliary parallel bars disposedover one surface of the grizzly and arranged at right angles to the barsto form a lattice, the openings of the lattice having a diagonaldimension smaller than the maximum width of projection of planarextraneous matter, the lattice being in the form of a rotatably drumwith the grizzly defining the inner periphery thereof and having scraperplates attached to the inner periphery, and an inlet for the waste glassand an outlet for the extraneous matter provided at the opposite ends ofthe lattice drum respectively.
 2. An apparatus as defined in claim 1wherein the parallel bars of the grizzly are annular bars arranged atright angles to the axial direction of the lattice drum, and theauxiliary parallel bars extend in the axial direction.
 3. An apparatusas defined in claim 1 wherein the parallel bars of the grizzly extend inthe axial direction of the lattice drum, and the auxiliary parallel barsare annular bars arranged at right angles to the axial direction.
 4. Anapparatus as defined in claim 1 wherein the lattice drum is installed inan inclined position with the outlet formed at the lower end thereof. 5.An apparatus as defined in claim 1 wherein the lattice drum is installedin a horizontal position and has a tapered shape with the outlet formedat the larger-diameter end thereof.